The present invention relates to a magnetizer comprising a permanent magnet having a shape of a hemisphere, a hemispherical shell, or a sphere, and more particularly, to a magnetizer comprising a permanent magnet having a shape of a hemisphere, a hemispherical shell, or a sphere capable of eliminating an overhang of a coil.
In general, a DC motor utilizes a repulsive force and an attractive force generated between a permanent magnet and a coil to which a current is applied. A commutator and a brush are connected to the coil. When a DC voltage is applied through the commutator and the brush to the coil in a magnetic field, the coil is rotated at the clockwise direction according to Fleming""s left hand law. Since the commutator and the brush have a function of supplying a unidirectional current to the coil, the coil is rotated at the one direction.
Permanent magnets used for the DC motor may be classified into several types of magnets according to price and material thereof. In addition, methods of magnetization are classified into a unidirectional magnetization and a radial magnetization. In addition, the magnetization can be implemented with multiple poles in some applications. The basic shapes of the permanent magnet include a cylinder, a cylindrical shell, a plate, and a hexahedron.
FIG. 1 is a view illustrating a structure of a conventional DC motor, and FIGS. 2a to 2b is a view for explaining a structure of a magnetization yoke which is adapted to the conventional DC motor.
As shown in FIG. 1, the DC motor comprises a case 1, a coil 2 which is disposed within the case 1, a permanent magnet 4 which is disposed within the coil2. The permanent magnet 4 has a central shaft 3. A air gap 5 is provided between the coil 4 and the permanent magnet 4.
In FIGS. 2a to 2d, two types of the conventional DC motors are illustrated according to the types of the permanent magnets. The one type of the permanent magnet shown in FIG. 2b in which the magnetic poles are disposed along the up-down direction corresponds to the structure of the magnetizer shown in FIG. 2a. The other type of the permanent magnet shown in FIG. 2d in which the magnetic poles are disposed along the radial direction corresponds to the structure of the magnetizer shown in FIG. 2c. 
In these magnetizers, reference numerals 1, 2, and 4 indicate the case, the coil, and the permanent magnet. In addition, reference numeral 6 indicates a non-magnetic member.
The DC motor, in which the magnetizer having one of the two types of the permanent magnets is provided, has a structural characteristic that the DC motor comprises a stator and a rotator, each of which has a cylindrical shape. The structural characteristic results in a problem that the coil has an inevitable end-winding overhang.
The overhang of the coil is never useful in generating a rotational force of the DC motor. Furthermore, the overhang may be a cause of copper loss or the other losses in the DC motor.
In order to solve the above mentioned problems, an object of the present invention is to provide a magnetizer comprising a permanent magnet having a shape of a hemisphere, a hemispherical shell, or a sphere capable of eliminating an overhang of a coil.
In order to achieve the object, an aspect of the present invention provides a magnetizer of a DC motor comprising: a case; a hemispherical permanent magnet provided within the case; a non-magnetic member provided below the hemispherical permanent magnet; and a coil provided to the non-magnetic member.
Another aspect of the present invention provides a magnetizer of a DC motor comprising: a case; a hemispherical-shell permanent magnet provided within the case; a non-magnetic member provided below the hemispherical-shell permanent magnet; and a coil provided to the non-magnetic member.
Further another aspect of the present invention provides a magnetizer of a DC motor comprising: a case; a spherical permanent magnet constructed with two hemispherical permanent magnets being arranged to face each other, the spherical permanent magnet being provided within the case; non-magnetic members provided below a upper one and above a lower one of the two hemispherical permanent magnets; and coils provided to the respective non-magnetic members.
In the above aspects of the present invention, the internal portion of the permanent magnet may be the one magnetic pole out of the N and S magnetic poles and the external portion of the permanent magnet may be the other magnetic pole.
In the above aspects of the present invention, the case may be made up of a ferromagnetic material.
In the above aspects of the present invention, distribution of the magnetic field may vary depending on the structure of the non-magnetic member.